The DNAs of a series of different chemically induced and spontaneously arising tumors have been applied to NIH3T3 mouse fibroblast cultures and observed to elicit foci of transformed cells. These transformed recipient cells thus have acquired a transmissible gene for transformation present in the donor cell from which the DNA was prepared. These cells can be placed in syngeneic mice in which they induce fibrosarcomas. Sera from these mice can then be used to immunoprecipitate antigens present in the transfected cells. One of these antigens may be the transforming protein encoded by the transforming gene. Such experiments have led to the detection of a protein induced specifically by the transforming genes of rat neuroblastomas. Another protein of 21,000 daltons is known to be associated with various human ras oncogenes and a third with the myc oncogene. The proposed work is designed to examine structural and enzymatic properties of these tumor proteins and how their expressions are regulated during cell growth and differentiation. (X)